The photovoltaic (PV) manufacturing process typically requires solar cells to be heated to extremely high temperatures. Traditional methods for heating involve utilizing conventional electric or infrared furnaces to heat the cells for long periods of time.
The heating process allows for the fabrication of the cells but is very expensive and results in impurities and imperfections in the PV cells.
The National Renewable Energy Laboratory (NREL), the only federal laboratory exclusively dedicated to the research, commercialization and development of renewable energy and energy efficiency technologies, has developed an optical furnace that may change the solar industry.
The optical furnace is able to heat PV cells more effectively at a fraction of the cost of traditional methods, which may result in a higher quality product at a lower cost.
The optical furnace is described in U.S. Patent Number 5,577,157, entitled “Optical Processing Furnace with Quartz Muffle and Diffuser Plate ” (’157 Patent) and U.S. Patent Application Number 2011/0003485, entitled “Optical Cavity Furnace for Semiconductor Wafer Processing” (’485 Application).
Figure 1 of the ’485 Application depicts an embodiment of the optical furnace. The furnace includes a bank of optical energy sources 12 a-n and reflectors 14 surrounding a transport system 22 enclosed in a cavity 18.
According to both the ’157 Patent and the ’485 Application, it is advantageous if the optical reflectors are made of a diffuse rather than a specular material. A diffuse reflector is advantageous because it ensures the optical energy is reflected evenly within the furnace cavity with a minimum of energy loss.
Figure 2 of the ’157 Patent shows another view of the optical furnace. The figure shows a bank of optical energy sources 21 above the furnace cavity 7. The cavity consists of a diffuse reflector box 15, 16, 17, 18 made of quartz, called the quartz box or muffle.
The figure also depicts a diffuser plate 9. The diffuser plate is also made of quartz and is placed on top of the quartz muffle in order to protect the muffle from the high energy released by the optical energy sources.
If the quartz muffle were to be damaged, replacement costs would be very high and the process would be time consuming. The diffuser plate is designed to be quickly and inexpensively replaced when damage occurs.
According to NREL, their optical furnace can potentially increase PV efficiency by four percentage points (from 16 to 20 percent). This would represent a major increase in efficiency.
Further, NREL is working in conjunction with AOS, Inc. to produce a manufacturing sized furnace. NREL anticipates this manufacturing furnace will be able to produce 1,200 highly efficient solar cells per hour. The increase in efficiency and manufacturer-scale production will all occur at a quarter of traditional PV manufacturing costs.
These improvements and reduced costs will hopefully mean better and less expensive PV cells on the market in the near future.
Article by David Gibbs, appearing courtesy Green Patent Blog.